Sputum induction as a method of analyzing pulmonary cells: reproducibility and acceptability

Charcot-Leyden crystal protein/galectin-10 is a surrogate biomarker of eosinophilic airway inflammation in asthma

Aim: Eosinophilic asthma is associated with more exacerbations and differential responses to treatment. The aim of this study was to assess if CLC/Gal-10 and MBP-1 are surrogate biomarkers of eosinophilic inflammation in asthma. Methods & results: Sputum induction was performed in patients with asthma and in healthy controls. Sputum analysis revealed higher (p < 0.001) levels of CLC/Gal-10 and MBP-1 in asthmatics versus healthy controls. CLC/Gal-10 levels were highly correlated (rs = 0.74; p < 0.001) with sputum eosinophils; MBP-1 approached significance (r = 0.44; p = 0.07). Conclusion: Increased CLC/Gal-10 and MBP-1 levels in the sputum were strongly correlated with sputum eosinophils in patients with asthma. CLC/Gal-10 and MBP-1 may be useful biomarkers for differentiation of eosinophilic airway inflammation in asthma.

Mediators in exhaled breath condensate after hypertonic saline challenge

BACKGROUND

Airway narrowing after hypertonic saline challenge (HSC) is postulated to be mediated by bronchoconstrictors and inflammatory mediators.

OBJECTIVE

To study the mechanism of this challenge by using exhaled breath condensate (EBC).

METHODS

Fifty-six subjects (9 to 72 years of age) performed an HSC, with EBC collection and exhaled nitric oxide (FENO) measurements before and after the challenge. Bronchial hyper-reactivity (BHR) was defined if forced expiratory volume in 1 second (FEV1) decreased by 10% compared with baseline (PD10). EBC volume was recorded and was analyzed for mucin, histamine, nitrite/nitrate, and pH.

RESULTS

Those with BHR had a significant rise in EBC volume/5-minute collection period after challenge (286.3 +/- 25.6 microl vs 402.2 +/- 31.3 microl, p = 0.0002), while BHR(-) subjects did not show this change (387.6 +/- 29.7 microl vs 364.1 +/- 30.1 microl, p = 0.55). FENO showed a significant decrease in both BHR(+) and BHR(-) groups after challenge (p = < 0.0001). In BHR(+) subjects histamine increased significantly (1.3 +/- 0.1 microM vs 1.5 +/- 0.1 microM, p = 0.006) compared with baseline, while EBC pH and mucin increased significantly after HSC in both groups. EBC nitrite did not change in either group.

CONCLUSION

EBC analysis suggests that HSC causes an increase in pH and mucin in both groups, but EBC volume and histamine only increased in the BHR(+) group. This suggests that mast cells are activated and fluid flux is associated with the positive response, while mucin release is independent of BHR in HSC.

Respiratory tract mucin genes and mucin glycoproteins in health and disease

This review focuses on the role and regulation of mucin glycoproteins (mucins) in airway health and disease. Mucins are highly glycosylated macromolecules (> or =50% carbohydrate, wt/wt). MUC protein backbones are characterized by numerous tandem repeats that contain proline and are high in serine and/or threonine residues, the sites of O-glycosylation. Secretory and membrane-tethered mucins contribute to mucociliary defense, an innate immune defense system that protects the airways against pathogens and environmental toxins. Inflammatory/immune response mediators and the overproduction of mucus characterize chronic airway diseases: asthma, chronic obstructive pulmonary diseases (COPD), or cystic fibrosis (CF). Specific inflammatory/immune response mediators can activate mucin gene regulation and airway remodeling, including goblet cell hyperplasia (GCH). These processes sustain airway mucin overproduction and contribute to airway obstruction by mucus and therefore to the high morbidity and mortality associated with these diseases. Importantly, mucin overproduction and GCH, although linked, are not synonymous and may follow from different signaling and gene regulatory pathways. In section i, structure, expression, and localization of the 18 human MUC genes and MUC gene products having tandem repeat domains and the specificity and application of MUC-specific antibodies that identify mucin gene products in airway tissues, cells, and secretions are overviewed. Mucin overproduction in chronic airway diseases and secretory cell metaplasia in animal model systems are reviewed in section ii and addressed in disease-specific subsections on asthma, COPD, and CF. Information on regulation of mucin genes by inflammatory/immune response mediators is summarized in section iii. In section iv, deficiencies in understanding the functional roles of mucins at the molecular level are identified as areas for further investigations that will impact on airway health and disease. The underlying premise is that understanding the pathways and processes that lead to mucus overproduction in specific airway diseases will allow circumvention or amelioration of these processes.

Sputum induction and bronchoscopy for assessment of ozone-induced airway inflammation in asthma

BACKGROUND

Neutrophilic airway inflammation, as defined by cell counts in respiratory tract lining fluid (RTLF), is a key end point in many studies of respiratory toxicity in both healthy and asthmatic subjects. BAL and sputum induction (SI) are the most common methods of sampling RTLF in such studies. However, the comparability of these methods (BAL and SI) after experimental treatment has not been investigated in a head-to-head controlled trial.

METHODS

To determine whether BAL and SI are comparable and can be used in place of each other in the assessment of neutrophilic airway inflammation after ozone (O(3)) exposure, we exposed 13 asthmatic subjects to either 0.2 ppm of O(3) or filtered air (FA) followed by either BAL or SI. Subjects then underwent the alternate (O(3) or FA) exposure followed by the same method of RTLF sampling. Next, subjects repeated the same exposure protocol with the alternate method of RTLF sampling. Differences in inflammatory indexes including the percentage of polymorphonuclear neutrophils (%PMNs) between the exposures were then correlated by regression analysis.

RESULTS

The %PMNs in sputum was poorly correlated with that in BAL fluid (R = 0.12). The correlation between the %PMNs in sputum and in the bronchial fraction of BAL (BFx) fluid, however, was somewhat higher (R = 0.50). Furthermore, the uncertainty of the estimate of %PMN values in BFx fluid and BAL fluid based on those of sputum values, using regression models, was almost as great as the magnitude of the O(3) effect itself (ie, 9.7% and 5.5% estimate errors for O(3) effects of 17.0% and 7.5%, respectively).

CONCLUSION

We concluded that SI and BAL indexes are not directly interchangeable in the assessment of O(3)-induced airway inflammation in asthmatic subjects.

Circadian variation of sputum inflammatory cells in mild asthma

BACKGROUND

Asthma, like many conditions, demonstrates a circadian rhythm with a worsening of lung function in the early morning hours compared with in the late afternoon.

OBJECTIVE

Because eosinophilic airway inflammation is a proposed mechanism for worsening asthma, we characterized circadian variation in airway eosinophils and determined its relationship to variability in airway function.

METHODS

Pulmonary function testing, sputum induction, and phlebotomy were performed at 7 am and 4 pm in 11 allergic subjects with mild asthma. Sputum was analyzed for cell viability, differential, and eosinophil-derived neurotoxin levels. IL-5 levels in serum were measured by means of ELISA.

RESULTS

Subjects had a significant decrease in FEV(1) (median [interquartile range] = 80% [70%-86%] vs 85% [82%-94%], P =.009) and a greater beta-agonist reversibility (median [interquartile range] = 13% [7%-32%] vs 8% [5%-14%], P =.024) in the early morning compared with in the late afternoon. Sputum analysis showed an increase in early morning total sputum leukocytes (median [interquartile range] = 4.3 x 10(6) [2.3 x 10(6) to 6.1 x 10(6)] vs 2.6 x 10(6) [1.7 x 10(6) to 3.6 x 10(6)], P =.044) and eosinophils (median [interquartile range] = 7.0 x 10(4) [2.7 x 10(4) to 18.7 x 10(4)] vs 3.6 x 10(4) [1.0 x 10(4) to 8.2 x 10(4)], P =.024). Furthermore, sputum eosinophils correlated with beta-agonist reversibility (R (s) = 0.665, P =.019). Finally, levels of IL-5 in serum and eosinophil-derived neurotoxin in sputum were significantly increased at 7 am.

CONCLUSION

These data suggest that circadian variability in pulmonary function in asthma could be related to changes in airway eosinophil recruitment and activation.

Induced sputum is a reproducible method to assess airway inflammation in asthma

To evaluate the reproducibility of induced sputum analysis, and to estimate the sample size required to obtained reliable results, sputum was induced by hypertonic saline inhalation in 29 asthmatic subjects on two different days. The whole sample method was used for analysis, and inflammatory cells were counted on cytospin slides. Reproducibility, expressed by intra-class correlation coefficients, was good for macrophages (+0.80), neutrophils (+0.85), and eosinophils (+0.87), but not for lymphocytes (+0.15). Detectable differences were 5.5% for macrophages, 0.6% for lymphocytes, 5.2% for neutrophils, and 3.0% for eosinophils. We conclude that analysis of induced sputum is a reproducible method to study airway inflammation in asthma. Sample sizes greater than ours give little improvement in the detectable difference of eosinophil percentages.

Safety and reproducibility of sputum induction in asthmatic subjects in a multicenter study

The safety of sputum induction and the reproducibility of measurements in induced sputum in multicenter studies is unknown. We examined the safety of sputum induction in a two-visit, six-center study in 79 subjects with moderate to severe asthma (mean +/- SD FEV(1) 71 +/- 12% predicted, 67% taking inhaled corticosteroids). In addition, we compared the reproducibility of markers of inflammation in induced sputum with the reproducibility of the FEV(1) and the methacholine PC(20). The FEV(1) decreased > or = 20% from the postbronchodilator baseline in 14% of all subjects and in 25% of subjects whose initial prebronchodilator baseline was 40 to 60% of predicted. All subjects responded promptly to additional albuterol treatment, and no subject developed refractory bronchoconstriction requiring treatment other than reversal of bronchospasm in the study laboratory. The reproducibility of measurements of the eosinophil percentage, eosinophil cationic protein, tryptase, and methacholine PC(20) were similar (concordance correlation coefficients of 0.74, 0.81, 0.79, and 0.74, respectively), without any significant among-center effect. We conclude that sputum induction can be performed safely in subjects with moderate to severe asthma in multicenter clinical trials when carried out under carefully monitored conditions. Importantly, we demonstrate that measurement of markers of inflammation in induced sputum is as reproducible as methacholine PC(20) and should prove useful in the assessment of airway inflammation in multicenter clinical trials.